In the manufacture of a semiconductor integrated circuit, various sheet-by-sheet processes such as a film forming process, an etching process, a heat treating process, a quality modification process and a crystallization process are repeatedly performed on a target object, e.g., a semiconductor wafer or the like, thereby forming a desired integrated circuit. While executing such processes, processing gases needed for the corresponding processes, e.g., a film formation gas or a halogen gas for the film forming process; an ozone gas or the like for the quality modification process; O2 gas, an inert gas such as N2 gas, or the like for the crystallization process, are respectively introduced into a processing chamber.
For example, in a sheet-by-sheet heat treatment apparatus for performing heat treatment on semiconductor wafers one by one, a mounting table incorporating therein, e.g., a resistance heater, is installed in a vacuum evacuable processing chamber. A semiconductor wafer is mounted on the top surface of the mounting table and is heated to a specified temperature (e.g., 100° C. to 1000° C.). In this state, a specified processing gas is introduced into the processing chamber to perform various heat treatments on the wafer under predetermined process conditions (see, e.g., Japanese Patent Laid-open Applications No. S63-278322, No. H07-078766, No. H03-220718, No. H06-260430, No. H08-78193 and No. 2004-356624). Therefore, those components arranged in the processing chamber are required to have heat-resistance with which the components resist the heating and corrosion-resistance with which the components are kept against corrosion even if they are exposed to the processing gases.
A mounting table structure for mounting thereon a semiconductor wafer is generally manufactured by thermally welding a mounting table together with a supporting column through, e.g., thermal diffusion bond technique. The mounting table is formed by embedding a resistance heater as a heating element in a ceramic material such as AlN or the like and then sintering them as a unit at a high temperature to ensure heat-resistance and corrosion-resistance and preventing metal contamination. The supporting column is also formed by sintering a ceramic material or the like in another process. The mounting table structure formed as a unit with the supporting column stands on a bottom portion of the processing chamber. Further, a quartz glass, which has heat-resistant and corrosion-resistance, may be used in place of the ceramic material.
Since the mounting table is formed by embedding the resistance heater as a heating element in the ceramic material or in the quartz glass and integrally sintering them as mentioned above, the mounting table structure as a whole has to be replaced with a new one only if a defect such as a partial fracture of the resistance heater or the like is generated in a part of the mounting table structure. This poses a problem in that the components other than the defective part also become useless.
Among the processes, there are a process particularly requiring a corrosion resistance, a process particularly requiring a resistance against a thermal shock and a process particularly requiring a resistance against metal contamination. Depending on the kinds of processes, there exist various specifications to comply with. In order to assure standardized use of parts, the mounting table structure is generally manufactured so as to cope with the most severe process in terms of the corrosion resistance, the heat resistance and the like. For that reason, depending on the kinds of processes used, a material having unnecessarily great resistances is selected as the material of the mounting table structure. Thus, the parts of the mounting table structure may suffer from over-specification. In particular, the parts having the increased resistances are costly to purchase and to process, so that an apparatus using the parts becomes expensive beyond necessity.
Since the supporting column is thermally bonded together with the bottom surface of the mounting table, the joint region of the mounting table and the supporting column exhibits increased heat conductivity, thus assuring superior heat transfer from the joint region to the supporting column. As a consequence, the joint region grows colder than the remaining portions of the mounting table, thereby creating a so-called cool spot where thermal stresses are concentrated. Therefore, the mounting table is easily cracked with the joint region as a starting point.
A thermocouple is attached to a rear surface of the mounting table in order to control the temperature of a heater of the mounting table. The thermocouple is attached after sintering the mounting table, and further, in order to prevent a detection line of the thermocouple from being exposed to a processing gas or other corrosive gases, only one thermocouple can be installed at the center portion of the rear surface of the mounting table to which the supporting column is joined. Therefore, there is no choice but to empirically find the temperature of the peripheral portion of the mounting table, although the temperature of the center portion of the mounting table can be measured by the thermocouple. For that reason, it may be impossible to keep improving the temperature uniformity of the mounting table or the in-plane temperature uniformity of the semiconductor wafer, in case where the heat radiation environment is changed to a great extent or in other cases.
When the resistance heater is integrally sintered in the mounting table, the pattern of the resistance heater is arranged in a calculated position with increased accuracy. However, the cross section of the resistance heater may be slightly deformed by the stresses generated during the sintering process. In this case, it is impossible to adjust the position of the resistance heater, which causes a difficulty to realize a temperature distribution as designed.